Pilot misinterprets ATC clearance and begins descent before cleared.

Attributes
ACN	337717
Time
Date	199605
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : tnv
State Reference	TX
Altitude	msl bound lower : 14500 msl bound upper : 15000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 225 flight time total : 7000 flight time type : 3000
ASRS Report	337717
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew
Supplementary
Air Traffic Incident	other
Situations
ATC Facility	procedure or policy : unspecified

Narrative:

Perceived clearance 'cleared direct HOAG1, coast 2 arrival, descend via the coast 2.' when reporting out of 15000 ft for 10000 ft we were told 'ok, but you were not cleared to descend, only to fly the route, descend now via the coast 2.' we had already descended to 14500 ft when the 'official' clearance was given. I asked and center advised of no conflict. An opinion: ATC needs to standardize verbiage regarding descent clearance associated with FMS arrs. Example: iah descent clearance -- 'cleared via the coast 2, descend via the coast 2.' however, at sna the clearance 'cleared for the sna east side 1 arrival' includes changes in altitude. The only way for pilots to know is to ask. We do, and their response is always the same 'of course,' or 'yes.' because of this we ask on every FMS arrival if we are cleared for the vertical portion. The only city I am aware of which specifically states clearance for descent is iah with their 'cleared to descend via the coast 2.' additionally, it is my belief that every arrival clearance includes altitude, but this is not done. Example: 'cleared for the das 2 arrival maintain (FL370/or pd X000 ft). The only time I perceive a problem is associated with the FMS arrival. Callback conversation with reporter revealed the following information: the reporter stated he was flying a B737-300. He stated that both the east side 1 at sna and the coast 2 at iah are FMS arrs.

Original NASA ASRS Text

Title: PLT MISINTERPRETS ATC CLRNC AND BEGINS DSCNT BEFORE CLRED.

Narrative: PERCEIVED CLRNC 'CLRED DIRECT HOAG1, COAST 2 ARR, DSND VIA THE COAST 2.' WHEN RPTING OUT OF 15000 FT FOR 10000 FT WE WERE TOLD 'OK, BUT YOU WERE NOT CLRED TO DSND, ONLY TO FLY THE RTE, DSND NOW VIA THE COAST 2.' WE HAD ALREADY DSNDED TO 14500 FT WHEN THE 'OFFICIAL' CLRNC WAS GIVEN. I ASKED AND CTR ADVISED OF NO CONFLICT. AN OPINION: ATC NEEDS TO STANDARDIZE VERBIAGE REGARDING DSCNT CLRNC ASSOCIATED WITH FMS ARRS. EXAMPLE: IAH DSCNT CLRNC -- 'CLRED VIA THE COAST 2, DSND VIA THE COAST 2.' HOWEVER, AT SNA THE CLRNC 'CLRED FOR THE SNA E SIDE 1 ARR' INCLUDES CHANGES IN ALT. THE ONLY WAY FOR PLTS TO KNOW IS TO ASK. WE DO, AND THEIR RESPONSE IS ALWAYS THE SAME 'OF COURSE,' OR 'YES.' BECAUSE OF THIS WE ASK ON EVERY FMS ARR IF WE ARE CLRED FOR THE VERT PORTION. THE ONLY CITY I AM AWARE OF WHICH SPECIFICALLY STATES CLRNC FOR DSCNT IS IAH WITH THEIR 'CLRED TO DSND VIA THE COAST 2.' ADDITIONALLY, IT IS MY BELIEF THAT EVERY ARR CLRNC INCLUDES ALT, BUT THIS IS NOT DONE. EXAMPLE: 'CLRED FOR THE DAS 2 ARR MAINTAIN (FL370/OR PD X000 FT). THE ONLY TIME I PERCEIVE A PROB IS ASSOCIATED WITH THE FMS ARR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED HE WAS FLYING A B737-300. HE STATED THAT BOTH THE E SIDE 1 AT SNA AND THE COAST 2 AT IAH ARE FMS ARRS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.